The prevalence of food allergy has been dramatically increasing for the last few decades. Food Allergy and Anaphylaxis Network (www.foodallergy.org) estimates that up to 15 million Americans have food allergies. Six to eight percent of children under the age of three have food allergies and nearly four percent of adults have them. Signs and symptoms of food allergy range from itching, hives, and diarrhea to life-threatening anaphylaxis. Currently, there is no cure for this disease, although allergen-specifc sublingual and oral immunotherapy (OIT) can successfully treat some patients. However, this therapy is associated with the risk of anaphylaxis and many patients resist the therapy. Thus, novel, innovative therapeutic and preventive measures are urgently needed. Histamine-releasing factor (HRF) is a secreted protein with the ability to activate mast cells and basophil in an IgE-dependent manner, while it has multiple intracellular functions. Our recent studies demonstrated that a subset of IgE and IgG molecules bind to HRF, leading to our discovery of specific inhibitors, N19 and H3 peptides, that blocked the HRF-immunoglobulin (Ig) interaction without affecting intracellular functions of HRF. A monomeric mutant of HRF, HRF-2CA, also inhibited the HRF-Ig interaction. In our unpublished study, prophylactic and therapeutic administration of N19 and HRF-2CA strongly reduced diarrhea occurrence and intestinal inflammation in an IgE/Fc?RI (high-affinity IgE receptor)-dependent mouse model of food allergy. Moreover, egg-allergic patients who exhibited high sensitivity to egg at the end of OIT, unlike those who did not, had higher levels of HRF-reactive IgE at 12 months than at 1 week after OIT initiation, suggesting the involvement of HRF-reactive IgE in human patients with egg allergy. These results collectively indicate that HRF-mediated activation of mast cells and basophils is involved in allergen-induced maximal intestinal inflammation. Based on these novel data, we will pursue HRF-based novel preventive and therapeutic modalities for the treatment of food allergy. To this end, we will optimize HRF-inhibitory peptides as an anti- fod allergy drug (Specific Aim 1). We will also investigate the mechanisms by which HRF inhibitors suppress food allergy, by identifying the cellular and molecular targets of HRF inhibitors in the murine food allergy model (Specific Aim 2). Therefore, completion of this study will allow us to determine which HRF inhibitor(s), i.e., N19, H3, related peptides (or modified peptides), or a combination thereof can be used to best prevent and/or treat food allergy. Positive results with HRF inhibitor(s) will lay the foundation for clinical studies in humans in the near future. In humans, HRF-based peptides will be used as preventive and/or therapeutic drugs as well as an adjuvant to be used together with OIT. Thus, this study has the potential to drastically change the clinical practice in food allergy.